3,1′-bridged 2-[2′-(4"-dialkylaminophenyl)ethenyl] pyrylium and 1-benzopyrylium dyes -: Synthesis and vis/NIR absorption/emission behaviour

A series of new 3,1'-bridged 2-[2'-(4 "-dialkylaminophenyl)ethenyl]-4,6-diarylpyrylium perchlorates (3), 2-[2'-(4 "-dialkylaminophenyl)ethenyl]-7-diethylamino-1-benzopyrylium perchlorates 5-8, 2-[4'-(4 "-dialkylaminophenyl)butadien-1',3'-yl]-, and 2-[2'-(7 "-diethylaminocoumar-3 "-yl)ethenyl]-7-diethylamino-1-benzopyrylium perchlorates 10-12 were synthesized and characterized by means of elemental analysis, m.p., Vis/NIR, and H-1 NMR spectra. Semiempirical MO calculations were performed to elucidate the essential features of the chromophores. The size of the bridging ring strongly affects the geometry of the chromophores which, in turn, determines the extent of charge transfer of the longest wavelength electronic transition. Increasing deviation from planarity causes the polymethine-like chromophore to become more polyene-like.